Fluoroelastomers, and more particularly, perfluoroelastomers are materials known for their high levels of chemical resistance, plasma resistance, acceptable compression set resistance and satisfactory mechanical properties. When high temperature or aggressive or harsh environments, such as corrosive fluids, solvents, lubricants, and oxidizing or reducing conditions are present in a process or end use environment, perfluoroelastomers are often selected. Perfluoroelastomers are typically formed by using perfluorinated monomers, including a perfluorinated cure site monomer, polymerizing the monomers and curing (cross-linking) the composition using a curing agent which reacts with the incorporated cure site monomer to form a material which exhibits elastomeric properties. Common cure site monomers include, among others, those having cyano cure sites. Examples of primary and secondary cyano-containing cure site monomers are known in the art. It is believed that in cure site monomers having cyano cure sites, certain curing agents trimerize the cyano cure sites that join to form triazine crosslinks.
Known curing agents include organometallic compounds and the hydroxides thereof, especially organotin compounds, including allyl-, propargyl-, triphenyl- and allenyl tin and the hydroxides. The tetraalkyltin compounds or tetraaryltin compounds, for example tetraphenyltin, are common. However, these curing agents provide a relatively slow rate of cure, are toxic and can introduce metallic contaminants to resulting elastomers.
Organic peroxides, e.g., dialkyl peroxides, are also known primary curing agents used with co-agents such as triallylisocyanurates for curing perfluoropolymers incorporating CH2x and other functional groups for crosslinking. Organic peroxide cures are typically more rapid than those noted above, and can provide better chemical resistance properties and good processability, but are relatively thermally unstable. Such peroxide and co-agent curing systems are known and are exemplified in U.S. Pat. No. 4,983,680. Similarly, the use of such curing systems in conjunction with a second, different curing system, so-called dual cure systems are also known, for example, U.S. Pat. No. 5,447,993 and WO 02/060969 A1.
Curing agents containing amino groups have also been employed. These include diamines and diamine carbamates, such as N,N′-dicinnamylidene-1,6-hexanediamine, trimethylenediamine, cinnamylidene trimethylenediamine, cinnamylidene ethylenediamine, and cinnamylidene hexamethylenediamine, hexamethylenediamine carbamate, bis(4-aminocyclohexyl)methane carbamate, 1,3-diaminopropane monocarbamate, ethylenediamine carbamate and trimethylenediamine carbamate.
Use of functionalized biphenyl-based curatives, such as 2,2-bis[3-amino-4-hydroxyphenyl]hexafluoropropane (“BOAP”) and its derivatives are known. Cures using these compounds tend to be slower to completion. Accordingly, these curatives may be used in concert with peroxide cure systems, resulting in a faster overall cure but having the known disadvantages of peroxide-containing system.
While such accelerated cure systems are an improvement, there always remains a need in the art for an improved curing agent capable of more quickly curing fluoroelastomers and perfluoroelastomers, particularly if additional use of a peroxide cure system is not an option. There is further a need in the art for a cure accelerator for perfluoroelastomer curatives that accelerates the cure rate of and maintains the beneficial properties of the elastomer, such as the sealing properties (low sticking) and the chemical and plasma resistant properties.